There are no companies that I trust entirely, but there certainly are those that I generally trust in different ways.
Nintendo: I trust that their main Mario, Mario Kart, SSB, and Zelda series will be great (almost never disappointed by that expectation)
Rockstar: I trust that their GTA series will always be superb
Blizzard Entertainment: I trust that their games will always be excellent (the only outright disappointment I remember was the outsourced Diablo I expansion that they no longer even acknowledge lol)
Naughty Dog: I pretty much just trust them to hit a home run with whatever they do, though the recent Uncharted was less than stellar and there has been a lack of innovation starting to show through.
Paradox Interactive: I trust that their home-developed Grand Strategy games will be fun and consume huge chunks of my life
I'm sure there's more, but that's all that came to mind so far.